diff --git a/config.h b/config.h
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+//======================================================================
+// config.h
+//======================================================================
+
+#ifndef __iop_config_h__
+#define __iop_config_h__
+
+// Uncomment to use the "factory" calibration mode.  This is intended to
+// allow calibration of IOP settings, separately from the uBITX/Raduino.
+// There will be no pass-thru of any CAT.
+#define FACTORY_CALIBRATION
+
+// IOPConfig
+// Used to store configuration parameters during runtime, as well as to
+// save them to EEPROM.
+struct IOPConfig {
+
+  // RECEIVE PARAMETERS
+
+  // rig-in parameters (RX)
+  uint8_t rxRigInLevel   = 5;
+  float   rxRigInVol     = 0.7;
+  float   rxRigInCal     = 1.0;
+  // USB-in parameters (RX) - debug/monitor use only
+  bool    rxUSBInEnable  = false;
+  float   rxUSBInVol     = 1.0;
+  float   rxUSBInCal     = 1.0;
+  // speaker-out (DAC) parameters (RX)
+  float   rxSpkrOutCal   = 1.0;
+  // line-out parameters (RX)
+  uint8_t rxLineOutLevel = 29;
+  float   rxLineOutCal   = 1.0;
+  // USB-out parameters (RX)
+  float   rxUSBOutCal    = 1.0;
+
+  // TRANSMIT PARAMETERS
+
+  // NOTE: Default rig-out parameters are based on trying to hit a 25mVrms output to the
+  // rig.  This is based on some discussion at the following URL:
+  //
+  // https://groups.io/g/BITX20/message/58951
+  // 
+  // This may or may not be totally applicable.  I believe it was for IMD/spurs on a pre-V5
+  // version of the uBITX.  So it may be OBE for my V5.  It also alludes to modifications
+  // to the transmit audio chain, which may be something I need to look into (i.e. increasing
+  // the gain on the initial mic pre-amp).
+  //
+  // Specifically, for the rig-out parameters:
+  //    line out level 31 = 1.16 V p-p
+  //                      = 0.58 V peak
+  //                      = 0.41 V rms = 410 mV rms
+  //    so output calibration needs to reduce that to 17.5 mV rms (70% of 25 mV rms)  
+  //           txMicInCal = 0.043 ... seems pretty low...
+  //
+  // Likewise, default line-in (TX) parameters assume consumer line level
+  // input, but with the default audio adaptor line-in level setting (5 = 1.33V p-p).
+  //    line in level 5 = 1.33 V p-p
+  //          signal in = 0.894 V p-p
+  //                    = 0.447 V peak
+  //                    = 0.316 V rms = 316 mV rms
+  //    so input calibration needs to convert that to the 410 mV noted above (equivalent
+  //    for the microphone), so that when that signal gets to the rig-out, it gets 
+  //    treated the same as the mic input.
+  //        txLineInCal = 1.30
+
+  // microphone-in parameters (TX)
+  uint8_t txMicInGain    = 12;
+  float   txMicInVol     = 0.7;
+  float   txMicInCal     = 1.0;
+  // line-in parameters (TX)
+  uint8_t txLineInLevel  = 5;
+  float   txLineInVol    = 0.7;
+  float   txLineInCal    = 1.30;
+  // USB-in parameters (TX)
+  float   txUSBInVol     = 0.7;
+  float   txUSBInCal     = 1.0;
+  // rig-out parameters (TX) - default settings are based on hitting 70% of 25mVrms w/ mic
+  uint8_t txRigOutLevel  = 29; //31;
+  float   txRigOutCal    = 1.0; //0.043;
+  // USB-out parameters (TX)- debug/monitor use only
+  bool    txUSBOutEnable = true;
+  float   txUSBOutCal    = 1.0; 
+};
+
+extern IOPConfig iopConfig;
+
+#endif
+
+//======================================================================
+// EOF
+//======================================================================